The invention pertains to a protective circuit and a method for protecting a circuit.
A protective circuit usually serves for protecting a terminal from electrostatic discharge, abbreviated as ESD. Integrated circuits used in automobiles feature protective circuits. Integrated circuits of this type are used, for example, in a Local Interconnect Network, abbreviated as LIN.
However, radiofrequency interference (radio interference) may occur during the operation and can be verified with a test method that is based on Direct Power Injection, abbreviated as DPI. The frequencies in the event of radiofrequency interference lie between 1 MHz and 1 GHz. The high voltage level and the fast crossings of a radiofrequency interference signal cause a conventional protective structure to be conductive and a current to flow through the protective structure. A conventional protective structure therefore also reacts to these frequencies in order to ensure a reliable dissipation during an ESD event. The relevant frequency range affecting a protective structure usually lies between 1 MHz and 100 MHz. A protective circuit therefore should not trigger in the event of radiofrequency interference in order to prevent a fault at a node of the LIN and loss of communication.
Document US 2009/0128969 A1 describes an adaptive protection against ESD for a LIN bus. A protective structure comprises a field effect transistor that couples a terminal to a reference potential terminal. In the event of radiofrequency interference, a control terminal of the field effect transistor is connected to the reference potential terminal.